Kaposi's sarcoma is a neoplastic disease associated with AIDS, and retroperitoneal fibromatosis is a disease of macaques that is related to Kaposi's sarcoma. In this project we investigated infections of rhesus and cynomolgus macaques with retroperitoneal fibromatosis-associated herpesvirus (RFHV). Animals infected with RFHV showed signs of lymphoproliferative disease and developed an unusual proliferative arteriopathy. Transfer of RFHV into cynomolgus macaques resulted in a rapidly fatal myeloproliferative disorder characterized by circulating multinucleated giant cells. We also attempted to infect pigtailed macaques with Kaposi's sarcoma-associated herpesvirus, but were unable to demonstrate productive infection in these animals.